Despite using every variant I could google for "Quick Lem" and "Kwik Lem," I'm trying to track down a bar sour mix with that (or similar name). Does this ring a bell for any of you?

I'm not looking for it because I think it is great, I am trying to match some bar's drink and I'm 90% sure that was the name on the concentrate he was using to make their sour mix. You know, the infamous Chinese bar yellow liquid that they pump into just about every drink they make. It is clearly not a liquor store item, it has the look of something that you get from a restaurant supply store.

Can't remember if it is a powder that you add water to or a liquid concentrate. But they used so much of the stuff, he mixed it up by the gallon jug then kept refilling his large "Finest Call" bottle with the plastic pour spout in his speed rail.

Maybe something similar to Lasco's Lemon Cocktail Powder Mix, from AceMart or Amazon? Or, Franco's Lemon Bar Mix, from Amazon. One bag makes one gallon of sour mix.
It also might be essentially the same as one of these, but private-branded and packaged for a local restaurant supply company.
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"The rum's the thing..."

Not easy to find even after getting the name right. There are only a handful of direct internet references to the product, mostly from bartending books. Thanks to the bartender giving me one of the empty pouches of mix, I was able to contact Tree-Ripe and have some shipped. It is made and distributed by Tree-Ripe Products, East Hanover, NJ. Surprisingly, it isn't on their product pages, even though they've been selling it for decades. They were nice enough not to make me buy it by the case, so I purchased a couple of pouches (about $4 ea, not including shipping). Each pouch makes a gallon.

A very good product. Unlike every other packaged/bottled sweet and sour mix I've tried, this one has a very good, very natural taste. Slightly creamy as if some "Orange Julius" powder was mixed in with a good lemonade. If you are using a sweet and sour mix in any of your drinks, I would strongly recommend this one.